Method and use for the prevention of fuel injector deposits

ABSTRACT

A method of substantially removing, or reducing the occurrence of, injector deposits in a diesel engine operated using a diesel fuel containing a minor amount of a metal-containing species is disclosed. The method includes adding to a diesel fuel the reaction product between a hydrocarbyl-substituted succinic acid or anhydride and hydrazine. The diesel engine is equipped with fuel injectors having a plurality of spray-holes, each spray-hole having an inlet and an outlet, and the fuel injectors have one or more of the following characteristics; (i) spray-holes which are tapered such that the inlet diameter of the spray-holes is greater than the outlet diameter; (ii) spray-holes having an outlet diameter of 0.10 mm or less; (iii) spray-holes where an inner edge of the inlet is rounded; (iv) 6 or more spray-holes; (v) an operating tip temperature in excess of 250° C.

This invention relates to a method for the removal or prevention of fuelinjector deposits in diesel engines, in particular to the removal orprevention of fuel injector deposits in modern diesel engines. Uses ofreaction products to remove or prevent fuel injector deposits andprocesses for the production of diesel fuel detergents are described.

There is continued legislative pressure to reduce emissions from dieselengines. In Europe by 2008, all new diesel engines must comply with theEuro V specification. This has resulted in the development of advancedfuel injection equipment characterised by fuel injectors which havecomplex spray-hole geometries, multiple and narrow spray-holes and whichoperate with high temperatures and pressures at the injector tips. As aconsequence of this increasing severity in operating conditions, theinjectors of modern common-rail diesel engines are prone to theformation of deposits. These deposits, which are found both inside andoutside the spray-holes of the injector nozzles, contribute directly toloss in engine power and increase in smoke production,

The formation of deposits on diesel fuel injectors is not a newphenomenon and historically any problem has been adequately addressed bythe use of conventional diesel detergent additives. It has been observedhowever, that the types of deposits formed under the more severeoperating conditions of engines which are being developed to be Euro Vcompliant are not adequately removed or prevented by conventional dieseldetergent additives. Although not wishing to be bound by any theory, itis presently thought that the formation of injector deposits in modernengines is exacerbated by the presence of minor amounts ofmetal-containing species in the fuel. Indeed, the Applicant's studieshave indicated that the use of fuels with negligible amounts ofmetal-containing contamination do not result in any significant problemswith deposits. However, normal diesel fuels will often contain low butmeasurable amounts of metal-containing contamination, for example, zinc,copper, iron and lead, and metal-containing species may also bedeliberately added to perform other functions. Analysis of the depositsformed in modern diesel engines indicates that, in addition to theexpected carbonaceous materials, metals such as zinc and copper can bedetected. The present invention specifically addresses the removal andprevention of these new types of injector deposits.

U.S. Pat. No. 3,375,092 discloses the product of the reaction between analkyl succinic acid or anhydride in which the alkyl radical has from 8to 24 carbon with a hydrazine. This product is said to be useful as ananti-icing additive for gasoline.

U.S. Pat. No. 2,640,005 discloses succinhydrazides which are formed forexample, by the reaction of hydrazine or hydrazine hydrate with theanhydride of a substituted succinic acid. These species are taught ashaving utility as fungicides.

U.S. Pat. No. 3,723,460 discloses that the species formed by thereaction of e.g. polyisobutenyl-substituted succinic acid or anhydridewith hydrazine can be used as fuel and motor oil additives. Theintermediate reaction products are preferably post-reacted with furthercompounds for example, those with displaceable halogens, alkylene oxidesetc., but may also be used alone. The species are discussed as being ofsufficient detergent strength to clean and maintain clean, a gasolineengine induction system but not of sufficient detergent strength topromote the formation of gasoline-in-water emulsions. They are also ableto function as a carburettor cleaner. There is no disclosure of use indiesel engine systems.

WO 2004/029183 discloses ashless anti-wear, anti-fatigue and extremepressure additives for lubricating oils. These have the formula:

where group R¹ may be e.g. alkyl and groups R²⁻⁴ may be hydrogen orsimilar to R¹. The additives are prepared by reacting e.g. an alkylsuccinic anhydride with hydrazine hydrate.

EP 0 632 123 A1 relates to diesel fuel compositions containingnitrogen-containing dispersants. The dispersant may be chosen from avery wide range of possible species, including those derived fromhydrazines. The dispersants are characterised in that the numericalvalue obtained by multiplying the percentage of nitrogen in thedispersant by the weight average molecular weight of the dispersant isbetween 45,000 and 100,000.

In accordance with a first aspect, the present invention provides amethod of substantially removing, or reducing the occurrence of,injector deposits in a diesel engine operated using a diesel fuelcontaining a minor amount of a metal-containing species, the methodcomprising adding to the diesel fuel the reaction product between ahydrocarbyl-substituted succinic acid or anhydride and hydrazine,wherein the diesel engine is equipped with fuel injectors having aplurality of spray-holes, each spray-hole having an inlet and an outlet,and wherein the fuel injectors have one or more of the followingcharacteristics:

-   -   (i) spray-holes which are tapered such that the inlet diameter        of the spray-holes is greater than the outlet diameter;    -   (ii) spray-holes having an outlet diameter of 0.10 mm or less;    -   (iii) spray-holes where an inner edge of the inlet is rounded;    -   (iv) 6 or more spray-holes;    -   (v) an operating tip temperature in excess of 250° C.

In accordance with a second aspect, the present invention provides theuse of the reaction product between a hydrocarbyl substituted succinicacid or anhydride and hydrazine to substantially remove, or reduce theoccurrence of, injector deposits in a diesel engine, the diesel enginebeing equipped with fuel injectors having one or more of characteristics(i) to (v) as defined in relation to the first aspect and operated usinga diesel fuel containing a minor amount of a metal-containing species.

In accordance with a third aspect, the present invention provides aprocess for producing a diesel fuel detergent effective to substantiallyremove, or reduce the occurrence of, injector deposition in dieselengine, the diesel engine being equipped with fuel injectors having oneor more of characteristics (i) to (v) as defined in relation to thefirst aspect and operated using a diesel fuel containing a minor amountof a metal-containing species, the process comprising reacting in asolvent, at least one hydrocarbyl-substituted succinic acid or anhydridewith hydrazine; refluxing the resulting reaction mixture to complete thereaction, and; raising the temperature of the reaction mixture to atleast 120° C., preferably at least 180° C., under reduced pressure andfor at least 30 minutes, preferably at least one hour.

It has been found that the reaction products used in the first andsecond aspects, and produced by the process of the third aspect, areparticularly effective at reducing the incidence of deposits in moderndiesel engine fuel injectors, and much more effective than the widelyused PIBSA-PAM detergents under similar conditions. It was surprising tonote however that in older type diesel engines, such as those used inthe industry standard XUD-9 detergency test, the reaction products ofuse in the present invention were outperformed by conventional PIBSA-PAMdetergents.

As discussed above, the incidence of injector deposits appears to beconnected to the presence of metal-containing species in the fuel. Somediesel fuels will contain no measurable metal content, in which case theincidence of injector deposits will be reduced. However, the presence orabsence of metal-containing species in diesel fuels is generally notapparent to the user and will vary with fuel production, even with fuelsfrom the same supplier. The present invention is thus useful in thoseinstances where metal-containing species are present and also as apreventative measure to lessen the impact of injector deposits whenre-fuelling with a fuel of unknown metal content.

In the context of all aspects of the present invention, substantialremoval of injector deposits should be taken to mean that deposits whichmay be present on the inside or outside of the spray-holes of theinjector nozzles are removed to the extent that the proper functioningof the injector is not significantly impaired. This may be determinedfor example by measuring increases in exhaust smoke or loss in enginetorque. It is not required that all traces of injector deposit areremoved. Similarly, a reduction in the occurrence of injector depositsdoes not require that no deposits whatsoever are formed, only again thatthe amount of any deposit which may form is not sufficient tosignificantly impair the proper functioning of the injector.

It is presently thought that the characteristics (i) to (v) of the fuelinjectors all contribute to the formation of injector deposits. It hasbeen observed that diesel engines employing fuel injectors which have aplurality of these characteristics are more prone to deposit formation.Thus in embodiments of the invention, the fuel injectors have two,preferably three, more preferably four, most preferably all five ofcharacteristics (i) to (v).

In a preferred embodiment, the fuel injectors have at leastcharacteristics (i) and (ii). In a more preferred embodiment, the fuelinjectors have at least characteristics (i), (ii) and (iii). In an evenmore preferred embodiment, the fuel injectors have at leastcharacteristics (i), (ii), (iii) and (iv).

The reaction between the hydrocarbyl-substituted succinic acid oranhydride and hydrazine produces a mixture of reaction products (asdiscussed hereinbelow). This mixture is made up from species which havea range of molecular weights. These range from low molecular weightspecies, being composed of one moiety of hydrocarbyl-substitutedsuccinic acid or anhydride and one or two moieties of hydrazine, tospecies composed of more than one moiety of hydrocarbyl-substitutedsuccinic acid or anhydride and one or more moieties of hydrazine. Theselatter species have relatively higher molecular weights than the former.It has been observed that most effective detergency is obtained byemploying a reaction product which contains a significant proportion ofhigher molecular weight species. Accordingly, it is advantageous that atleast 25%, preferably at least 50%, most preferably at least 80% byweigt of the reaction product between the hydrocarbyl-substitutedsuccinic acid or anhydride and hydrazine has a molecular weight which ismore than 2 times, preferably more than 2.5 times, the average molecularweight of the hydrocarbyl group of the hydrocarbyl-substituted succinicacid or anhydride.

Expressed in terms of EP 0 632 123 A1 discussed above, preferably, thereaction product of the present invention is such that the numericalvalue obtained by multiplying the percentage of nitrogen in the productby the weight average molecular weight of the product is in excess of105,000, more preferably in excess of 110,000, for example between110,000 and 250,000.

The various features of the invention, which are applicable to allaspects will now be described in more detail.

(a) The Reaction Product

This comprises the product of the reaction between ahydrocarbyl-substituted succinic acid or anhydride and hydrazine.

(i) Hydrocarbyl-Substituted Succinic Acid or Anhydride.

As used in this specification the term “hydrocarbyl” refers to a grouphaving a carbon atom directly attached to the rest of the molecule andhaving a hydrocarbon or predominantly hydrocarbon character. They may besaturated or unsaturated, linear or branched. Preferably, thehydrocarbyl groups are hydrocarbon groups. These groups may containnon-hydrocarbon substituents provided their presence does not alter thepredominantly hydrocarbon character of the group. Examples include keto,halo, nitro, cyano, alkoxy and acyl. The groups may also oralternatively contain atoms other than carbon in a chain otherwisecomposed of carbon atoms. Suitable hetero atoms include, for example,nitrogen, sulphur, and oxygen. Advantageously, the hydrocarbyl groupsare alkyl groups.

Preferably, tie hydrocarbyl group of the hydrocarbyl-substitutedsuccinic acid or anhydride comprises a C₈-C₃₆ group, preferably a C₈-C₁₈group. Non-limiting examples include dodecyl, hexadecyl and octadecyl.Alternatively, the hydrocarbyl group may be a polyisobutylene group witha number average molecular weight of between 200 and 2500, preferablybetween 800 and 1200. Mixtures of species with different lengthhydrocarbyl groups are also suitable, e.g. a mixture of C₁₆-C₁₈ groups.

The hydrocarbyl group is attached to a succinic acid or anhydride moietyusing methods known in the art. Additionally, or alternatively, suitablehydrocarbyl-substituted succinic acids or anhydrides are commerciallyavailable e.g. dodecylsuccinic anhydride (DDSA), hexadecylsuccinicanhydride (HDSA), octadecylsuccinic anhydride (ODSA) andpolyisobutylsuccinic anhydride (PIBSA).

(ii) Hydrazine

Hydrazine has the formula:NH₂—NH₂

Hydrazine may be hydrated or non-hydrated. Hydrazine monohydrate ispreferred.

(iii) Reaction of (i) and (ii)

The reaction between the hydrocarbyl-substituted succinic acid oranhydride and hydrazine produces a variety of products. As noted above,it is preferable for good detergency that the reaction product containsa significant proportion of species with relatively high molecularweight. The precise nature of the species produced in the reaction hasnot yet been fully elucidated however, it is presently thought that amajor high molecular weight product of the reaction is an oligomericspecies predominantly of the structure:

where n is an integer and greater than 1, preferably between 2 and 10,more preferably between 2 and 7, for example 3, 4 or 5. Each end of theoligomer may be capped by one or more of a variety of groups. Somepossible examples of these terminal groups include:

Alternatively, the oligomeric species may form a ring having no terminalgroups:

Also thought to be present is a species of the structure:

where R′ represents the hydrocarbyl substituent. It should be note thatit is also within the scope of the present invention to use more thanone hydrocarbyl-substituted succinic acid or anhydride in which case thegroups R′ in the above structures may be different from one another.

Both of the above structures contain at least two moieties derived fromthe hydrocarbyl-substituted succinic acid or anhydride. The molecularweights of these species are thus more than twice the average molecularweight of the hydrocarbyl substituent R′. In the context of the presentinvention the species are thus of relatively high molecular weight.

As lower molecular weight reaction products, species of the followingstructures are also thought to be present:

Further possible minor products include;

There may also be some salt formation resulting in species of thefollowing structures:

The general synthesis of the reaction products used in the presentinvention has been described in the art, for example, U.S. Pat. No.3,375,092, U.S. Pat. No. 2,640,005 and U.S. Pat. No. 3,723,460 citedhereinabove. A range of possible reaction schemes and products has alsobeen given by Feuer et al., in Jn. Amer. Chem. Soc, 73 (1951) pp.4716-4719. By way of example a possible preparative route is as follows.

A charge of alkyl-substituted succinic anhydride together with an equalweight of solvent, e.g. toluene is heated to ca. 50° C. under nitrogen.The desired amount of hydrazine hydrate is added drop-wise causing anexotherm. Once addition is complete, the reaction mixture is heated toreflux for several hours. The mixture is then water/solvent stripped andthe temperature raised to 180° C. under reduced pressure.

Preferably, the hydrocarbyl-substituted succinic acid or anhydride andhydrazine are reacted in a molar ratio of between 2:1 and 1:4, morepreferably between 1:1-1:3.

Preferably, the reaction product between the hydrocarbyl-substitutedsuccinic acid or anhydride and hydrazine is added to the diesel fuel inan amount of between 10 and 500 ppm by weight, based on the weight ofthe fuel, more preferably between 20 and 100 ppm.

(b) The Diesel Fuel

Preferably, the diesel fuel is a petroleum-based fuel oil, especially amiddle distillate fuel oil. Such distillate fuel oils generally boilwithin the range of from 110° C. to 500° C., e.g. 150° C. to 400° C. Thefuel oil may comprise atmospheric distillate or vacuum distillate,cracked gas oil, or a blend in any proportion of straight run andthermally and/or refinery streams such as catalytically cracked andhydro-cracked distillates.

Other examples of diesel fuels include Fischer-Tropsch fuels.Fischer-Tropsch fuels, also known as FT fuels, include those describedas gas-to-liquid (GTL) fuels, biomass-to-liquid (BTL) fuels and coalconversion fuels. To make such fuels, syngas (CO+H₂) is first generatedand then converted to normal paraffins by a Fischer-Tropsch process. Thenormal paraffins may then be modified by processes such as catalyticcracking/reforming or isomerisation, hydrocracking andhydroisomerisation to yield a variety of hydrocarbons such asiso-paraffins, cyclo-paraffins and aromatic compounds. The resulting FTfuel can be used as such or in combination with other fuel componentsand fuel types. Also suitable are diesel fuels derived from plant oranimal sources such as FAME. These may be used alone or in combinationwith other types of fuel.

Preferably, the diesel fuel has a sulphur content of at most 0.05% byweight, more preferably of at most 0.035% by weight, especially of atmost 0.015%. Fuels with even lower levels of sulphur are also suitablesuch as, fuels with less than 50 ppm sulphur by weight, preferably lessthan 20 ppm, for example 10 ppm or less.

As discussed herein, the Applicants have observed that the problemsassociated with the formation of injector deposits in engines beingdeveloped to be Euro V compliant are associated with the presence ofmetal-containing species in the diesel fuel. Commonly when present,metal-containing species will be present as a contaminant, for examplethrough the corrosion of metal and metal oxide surfaces by acidicspecies present in the fuel. In use, fuels such as diesel fuelsroutinely come into contact with metal surfaces for example, in vehiclefuelling systems, fuel tanks, fuel transportation means etc. Typically,metal-containing contamination will comprise metals such as zinc, iron,copper and lead.

In addition to metal-containing contamination which may present indiesel fuels there are circumstances where metal-containing species maydeliberately be added to the fuel. For example, as is known in the art,metal-containing fuel-borne catalyst species may be added to aid withthe regeneration of particulate traps. Such catalysts are often based onmetals such as iron, cerium Group I and Group II metals e.g., calciumand strontium, either as mixtures or alone. Also used are platinum andmanganese. The presence of such catalysts may also give rise to injectordeposits when the fuels are used in engines being developed to be Euro Vcompliant.

Metal-containing contamination, depending on its source, may be in theform of insoluble particulates or soluble compounds or complexes.Metal-containing fuel-borne catalysts are often soluble compounds orcomplexes or colloidal species. It will be understood thatmetal-containing species in the context of the present invention includeboth species which are metallic and those where the metal constituent isin compounded form.

In an embodiment, the metal-containing species comprises a fuel-bornecatalyst.

In a preferred embodiment, the metal-containing species comprises zinc.

Typically, the amount of metal-containing species in the diesel fuel,expressed in terms of the total weight of metal in the species, isbetween 0.1 and 50 ppm by weight, for example between 0.1 and 10 ppm byweight, based on the weight of the diesel fuel.

(e) Fuel Injector Characteristics

Historically, diesel engine fuel injectors have been simple in design.In recent years, the connection between injector design and engineperformance has become better understood. For example, the knowledgethat a fine distribution of fuel droplets promotes a decrease inemissions has led to a gradual narrowing of fuel injector spray-holesand increased injector pressures. As mentioned hereinabove, the drive tomeet the upcoming Euro V emissions specification has led to furtheradvances in fuel injector design.

(i) Tapered Spray-Holes

The majority of fuel injectors have spray-holes which are uniform incross-section. In the present invention, preferably the spray-holes aretapered such that diameter at the point where the fuel enters thespray-hole (the inlet) is greater than the diameter at the point wherethe fuel exits the spray-hole (the outlet). Most typically, thespray-holes will be conical or frusto-conical in shape.

(ii) Spray-Hole Diameter

The spray-holes preferably have an outlet diameter of 0.1 mm or less,more preferably 0.08 mm or less. This may be compared to injectors of 10to 15 years ago which had spray-holes of typically 0.25 mm.

(iii) Rounded Spray-Holes

In the context of the present invention, rounded spray-holes are thosewhere the inner edge of the inlet of the hole has been formed, smoothedor eroded to have a curved or radial profile, rather than an angledprofile.

(iv) Multiple Spray-Holes

Historically, fuel injectors have had up to four spray-holes. Thepresent invention relates to fuel injectors preferably having 6 or morespray-holes, for example 6, 7, 8, 9, 10 or more. It is anticipated thatfuture designs of fuel injectors will have even more spray-holes.

(V) Operating Tip Temperature

The combination of lower fuel flow due to a large number of spray-holes,higher fuel pressures and complex spray-hole geometry leads to increasedinjector tip temperatures. Typically, the fuel injectors will have anoperating tip temperature in excess of 250° C., preferably in excess of300° C. It will be understood that the operating tip temperature of thefuel injectors refers to the temperature of the injector tip duringnormal running of the diesel engine. Those skilled in the art will beaware of methodologies to measure the injector tip temperature, forexample by the use of suitably placed thermocouples.

Characteristics (i) to (iv) result in a less turbulent fuel flow throughthe injector. Whilst this is generally advantageous, it lessens thepossibility for the fuel to physically erode any deposits which may bepresent. The increase in operating tip temperature is also thought tocontribute to the formation of deposits.

It has also been observed that the reaction products which are thesubject of the present invention are effective to improve the lubricityof low sulphur-content diesel fuels. The reaction product ofdodecyl-substituted succinic anhydride and hydrazine was found to beparticularly effective in this regard.

The invention will now be described by way of example only.

Preparative Routes

EXAMPLE 1

Dodecylsuccinic anhydride (200 g, 0.75 mol) was weighed into a 11, threeneck, round-bottom flask together with toluene (200 g). Under nitrogenand with stirring, the temperature was raised to ca. 50° C. andhydrazine monohydrate (37.59 g, 0.75 mol) added dropwise. Once additionwas complete, the mixture was heated to reflux for 5 hours. Toluene wasremoved at 40° C. until no more bubbling was seen and then the productwas held for 1 hour at 0 mbar and 40° C.

The product produced in the reaction contained around 10% by weight ofspecies having a molecular weight more than 2 times the molecular weightof the hydrocarbyl group of the dodecylsuccinic anhydride reactant.

EXAMPLE 2

Dodecylsuccinic anhydride (200 g, 0.75 mol) was weighed into a 11, threeneck, round-bottom flask together with toluene (200 g). Under nitrogenand with stirring, the temperature was raised to ca. 50° C. andhydrazine monohydrate (112.76 g, 2.25 mol) added dropwise. Once additionwas complete, the mixture was heated to reflux for 5 hours. Toluene wasremoved at 40° C. until no more bubbling was seen and then he productwas held for 4 hours at 0 mbar and 180° C.

The product produced in the reaction contained around 70% by weight ofspecies having a molecular weight more than 2 times the molecular weightof the hydrocarbyl group of the dodecylsuccinic anhydride reactant.

EXAMPLE 3

A further example using dodecylsuccinic anhydride in a synthesis similarto Example 2 produced a product containing around 84% by weight ofspecies having a molecular weight more than 2 times the molecular weightof the hydrocarbyl group of the dodecylsuccinic anhydride reactant.

Effect of Process Variables

Example 2 was repeated varying the temperature and pressure of the finalstage following the removal of toluene. Table 1 below shows the effectof these variables on the molecular weight distribution of the productsobtained. In the Table, high MW species are those having a molecularweight more than 2 times the molecular weight of the hydrocarbyl groupof the dodecylsuccinic anhydride reactant. TABLE 1 Temperature/° C.Pressure/mbar % of high MW species 40 35 20 60 35 15 80 35 17 100 35 18120 35 25 140 35 33 160 35 46 180 35 62 180 0 76

Following the routes of Examples 1 and 2, further species were preparedby reacting hydrazine mono-hydrate with a C₂₄-alkyl succinic anhydrideand a polyisobutylene-substituted succinic anhydride (mol weight of PIBca. 1000).

Test Protocol

The protocol used is described by Graupner et al. “Injector deposit testfor modern diesel engines”, Technische Akademie Esslingen, 5thInternational Colloquium, 12-13 Jan. 2005, 3. 10, p 157, Edited byWilfried J Bartz. Briefly, the protocol aims to replicate the operatingconditions in a modern diesel engine with an emphasis on the fuelinjector tip. The test is split into five stages:

-   -   a) an iso-speed measurement of engine power output    -   b) an 8 hour endurance    -   c) an extended soaking period (3 to 8 hours) during which the        engine is stopped and allowed to cool    -   d) a second 8 hour endurance run    -   e) an iso-speed measurement of engine power output.

For the data presented herein, the five stages above were used however,stages b), c) and d) can be repeated any number of times to suit thetesting programme being undertaken. Also, stages a) and e) may beomitted but are useful to improve understanding of the results. Resultsare reported as the difference between the average torque at the startof the test during stage a) and the average torque at the end of thetest during stage e). Alternatively, if the isospeed procedure is notrun, the measured difference between starting torque at fall load/fullspeed and final load/speed can be used. Differences in smoke productionare also noted. The formation of injector deposits will have a negativeinfluence on the final power output and will increase the amount ofsmoke observed. The injectors used had the physical characteristics(i)-(v) described above.

To replicate the conditions expected in a modern diesel engine, a smallamount of metal contamination in the form of zinc neodecanoate was addedto the fuel used to run the engine.

The fuel used was a low-sulphur content diesel fuel with thecharacteristics shown in Table 2 below. TABLE 2 Test description ValueUnits sulphur content 0.0005 mass % cetane number 55.4 — density @ 15°C. 844.9 kgm⁻³ distillation characteristics D5% 204.8 ° C. D10% 211.6 °C. D20% 222.2 ° C. D30% 232.2 ° C. D40% 242.1 ° C. D50% 252.3 ° C. D60%262.8 ° C. D70% 275.1 ° C. D80% 290.5 ° C. D90% 315.1 ° C. D95% 337.1 °C. FBP 353.6 ° C. IBP 179.7 ° C. kinematic viscosity @ 20° C. 3.935 cStkinematic viscosity @ 40° C. - D445 cloud point −14.0 ° C. CFPP −33.0 °C.

For comparative purposes, the species of the invention were tested inthe industry standard XUD9 detergency test. A commercial PIBSA-PAMdetergent was tested also. The results are given in Table 3 below. TABLE3 Treat rate Needle lift in Species wppm (active ingredient) XUD9Untreated fuel — 92 PIBSA-PAM 30 57 PIBSA-PAM 60 53 PIBSA-PAM 100 8PIBSA-PAM 279 14 Example 1 60 83 Example 2 60 83 Example 3 60 93 PIB1000hydrazide 60 77 C₂₄-SA hydrazide 60 78 Example 2 300 83 PIB1000hydrazide 300 76

These results show that the commercial PIBSA-PAM detergent gave theexpected excellent performance in the XUD-9 test. Contrastingly, thehydrazine species performed poorly, even at high treat rates.

The species were then tested using the test protocol described above.Results are given in Table 4 below. 3 ppm of Zn in the form of zincneodecanoate was added to the fuel for all tests (except for theuntreated fuel alone). TABLE 4 Treat rate wppm Species (activeingredient) Torque loss Untreated fuel — 4.3% Untreated fuel + 3 ppm Zn— 17.2% PIBSA-PAM 60 13.7% PIB1000 hydrazide 60 9.7% C₂₄-SA hydrazide 607.1% Example 1 60 12.0% Example 2 60 5.2%

Table 5 below shows a further result for the product of Example 3. TABLE5 Treat rate wppm Species (active ingredient) Torque loss Untreated fuel— 1.3% Untreated fuel + 3 ppm Zn — 10.0% PIBSA-PAM 60 9.2% Example 3 600.9%

The results show that the addition of zinc to the untreated fuel givesrise to a large increase in torque loss. The commercial PIBSA-PAMdetergent only gave a marginal improvement. All hydrazine speciesprovided a greater improvement than the commercial detergent.Particularly good performance was obtained for the species of Example 2and Example 3 which both contained a high proportion of the highermolecular weight species.

The results in Table 6 below also illustrate the effect of the molecularweight distribution of the species on torque loss. Again, all testscontained 3 ppm of Zn in the form of zinc neodecanoate. The species usedwere the products of the reaction between dodecylsuccinic anhydride andhydrazine mono-hydrate following the routes of Examples 1 and 2 aboveand were present in the fuel at 60 wppm. TABLE 6 % of high MW speciesTorque loss 90.0 0.1% 73.4 4.2% 72.0 5.2% 70.0 5.2% 10.0 12.0%

These results confirm the increased effectiveness of the materials whichcontain the highest percentage of higher molecular weight species.

1. A method of substantially removing, or reducing the occurrence of,injector deposits in a diesel engine operated using a diesel fuelcontaining a minor amount of a metal-containing species, the methodcomprising adding to the diesel fuel a reaction product between ahydrocarbyl-substituted succinic acid or anhydride and hydrazine,wherein the diesel engine is equipped with fuel injectors having aplurality of spray-holes, each spray-hole having an inlet and an outlet,and wherein the fuel injectors have one or more of the followingcharacteristics: (i) spray-holes which are tapered such that the inletdiameter of the spray-holes is greater than the outlet diameter; (ii)spray-holes having an outlet diameter of 0.10 mm or less; (iii)spray-holes where an inner edge of the inlet is rounded; (iv) 6 or morespray-holes; (v) an operating tip temperature in excess of 250° C.
 2. Amethod according to claim 1 wherein the fuel injectors have two or moreof characteristics (i) to (v).
 3. A method according to claim 2 whereinthe fuel injectors have at least characteristics (i) and (ii).
 4. Amethod according to claim 1 wherein at least 25% by weight of thereaction product between the hydrocarbyl-substituted succinic acid oranhydride and hydrazine has a molecular weight which is more than 2times the average molecular weight of the hydrocarbyl group of thehydrocarbyl-substituted succinic acid or anhydride.
 5. A methodaccording to claim 1 wherein the hydrocarbyl group of thehydrocarbyl-substituted succinic acid or anhydride comprises a C₈-C₃₆group or a polyisobutylene group with a number average molecular weightof between 400 and
 2500. 6. A method according to claim 1 wherein thehydrocarbyl-substituted succinic acid or anhydride and hydrazine arereacted in a molar ratio of 2:1-1:4.
 7. A method according to claim 1wherein the reaction product between the hydrocarbyl-substitutedsuccinic acid or anhydride and hydrazine is added to the diesel fuel inan amount of between 10 and 500 ppm by weight based on the weight of thefuel.
 8. A method according to claim 1 wherein the metal-containingspecies comprises zinc, copper, iron, lead, cerium, a Group I or IImetal, platinum or manganese.
 9. A method according to claim 8 whereinthe metal-containing species comprises zinc.
 10. A method according toclaim 1 wherein the metal-containing species comprises a fuel-bornecatalyst.
 11. A method according to claim 1 wherein the amount ofmetal-containing species in the diesel fuel, expressed in terms of thetotal weight of metal in the species, is between 0.1 and 50 ppm byweight based on the weight of the diesel fuel.
 12. A process forproducing a diesel fuel detergent effective to substantially remove, orreduce the occurrence of, injector deposits in diesel engine, comprisingreacting in a solvent, at least one hydrocarbyl-substituted succinicacid or anhydride with hydrazine; refluxing the resulting reactionmixture to complete the reaction; and raising the temperature of thereaction mixture to at least 120° C. under reduced pressure and for atleast 30 minutes.